1. Field of the Invention
The present invention relates to mining of different kinds of power generating fossils and can be used in coal, shale mining, and other branches of mining industry connected to solid fuel consumers via transportation infrastructure facilities.
2. Description of Related Art
The traditional method of providing various consumers with coal or another solid mineral fuel is well known. To this end, the run-of-mine coal is delivered to the earth surface storage by skip hoists and concentrated at a coal-concentrating plant. Then, thus produced high-quality solid fuel is shipped from the finished product storage to the consumer via railway transport.
Cleaned coal arrived to the destination point is discharged from cars, piled up at open areas, and then delivered for its direct application (see, e.g., Golitsyn M. V., M. B Golitsyn A. M. Everything About Coal. Moscow, Nauka Publishers, 1989.-192 pp.)
The above production string includes several storage operations, which is necessary due to cyclic character of mine skip hoists operation and railroad transportation mode.
However, the overwhelming majority of consumers introduce solid fuel into their processes continuously, rather than periodically and, what is more, at high rates. For example, the coal consumption of a modern fuel-burning power plant is measured by hundreds, and sometimes by thousands tons per. Accordingly, to avoid the hazard of power generation interruption, especially in winter periods characterized by peak power consumption accompanied with not infrequent coal delivery irregularities due to snow banks, the open fuel stores can reach hundreds of thousands and even millions tons.
However, coal, in contrast to quartz sand, is not a chemically inert material and it cannot be stored out of doors as long as is wished without losing its consumer properties.
In the course of railroad transportation and during the out-of-door storage, the irreversible processes of coal oxidation by the air oxygen are started and developed. By this reason, huge piles of coal become the source of regularly occurring fires, to say nothing of the fact that even without combustion, the irreversible endogenous oxidation processes of coaly substance taking place in such coal piles decrease substantially the calorific value of coal, which results in the increase of solid fuel demand and consequently, to a significant drop in power production efficiency.
Besides, The accumulation of such huge volumes of coal means, in essence, the formation of secondary, this time, anthropogenic coal deposits. The delivery of fuel for combustion from such ‘deposits’, especially in winter, when coal loses its flowability and fuses into a frozen monolith, becomes no less, and sometimes even more cumbersome than mining from natural deposits, where the coal brittleness remains unchanged over the entire course of coal field development.
In winter, no less daunting problem is coal discharge from railroad cars, especially when wet concentration methods are used. Coal fuses into a frozen mass and forms a single lump with the car.
Thus, the use of railroad transport for solid fuel delivery, in particular, to large power plants, especially in winter, results in the necessity of dual mining: first, from a natural deposit and then, from an artificial, anthropogenic ‘deposit’.
Apart from the irreversible loss of a substantial fraction of coal consumer value, the intermediate storage and railroad transportation of coal together with numerous handling operations throughout the whole process, from the mine coalface to the power plant boiler furnace, result in significant mechanical losses of flowable material due to intense dusting. In fact, only coal blowing by wind during railroad transportation results in losses of 2 to 5 tons of coal per car, depending on coal coarseness, weather, and train speed.
Besides huge economical losses, with regard for the fact that annual world coal production is measured by billions of tons, the coal dust ingress into environment represents a serious ecological and pressing sanitary problem, in particular, for communities located in the immediate vicinity of coal dusting sites.
A method closest to the present invention from the viewpoint of technical essence and effect produced is the use of aqueous magnetite suspension for coal concentration and subsequent transportation to the destination point (see, in particular, the U.S. Pat. No. 5,169,267).
The use of aqueous magnetite suspension as a carrier medium for coal transportation via pipeline allows to eliminate the railroad transport services and to create an integrated stream-handling concentration and transportation process. The large-sized solid fuel is processed at a gravity coal-concentrating plant and delivered directly to a destination point using the pipeline transportation only. Note that the use of magnetite suspensions for coal beneficiation is well established and the most commonly encountered beneficiation method in the world coal mining industry.
However, the magnetite density (5.2-5.5 g/cm3) exceeds that of coal (1.3-1.5 g/cm3) by several times. By this reason, this artificial heavy medium, aqueous magnetite suspension, which is unstable under stationary conditions, cannot be used for the separation of coal from waste rock under these conditions. Even storage of this suspension, to say nothing of any beneficiation processes, requires intense mixing to prevent magnetite deposition. However the stable maintenance of magnetite in suspended state by constant agitation requires continuous power consumption. Besides, the intense agitation mode maintained in various separation devices prevents from clear separation of particles with close densities representing aggregates of coal with waste rock. This results in inevitable contamination of coal concentrate with mineral impurities, as well as coaly substance carryover to dump together with dressing tails; this is especially true for coarse fractions of material being processed. Therefore, a deep beneficiation of coal requires breaking of aggregates achieved by the continuation of grinding.
However, with the size reduction of raw material, the size of suspensoid particles used for the preparation of heavy medium becomes more and more, comparable with that of minerals to be separated.
As a result, the role of fluid used for the separation of fine-dispersed material plays water itself, rather than heavy suspension. However, the density of water is too small to provide the efficient lamination of minerals constituting the raw material. By this reason the coal beneficiation using heavy magnetite suspensions does not represent a universal beneficiation process. This leads to the necessity of using flotation at coal concentrating plants for the concentration of coal fines, which may constitute up to one third of total mine mass volume, bearing in mind modern means of mining face winning mechanization.
However, the flotation beneficiation methods are by an order of magnitude more expensive than the gravity methods. Besides, stockpiling of coal flotation beneficiation tailings nearby the coal concentrating plant remains a heavy ecological problem still waiting for solution, which would be satisfactory from all viewpoints.
The discrete structure of magnetite suspension prevents from using such heterogeneous media as heavy liquids for hydrostatic lift of coal from the mine to earth surface by direct floating-up in a vertical well filled with this heavy medium: under stationary conditions, when liquid is at rest, magnetite irreversibly precipitates in such a vertical column several hundred meters high, liquid loses heavy medium properties, and a dense magnetite plug is formed at the bottom of this pipeline.
Under high stream turbulization conditions taking place in trunk pipelines, magnetite may precipitate in the case of force-majeure events only, e.g., pumping station power supply failure, terrorist attacks, etc.
However, in any case, the use of magnetite suspension as a carrier medium in long distance pipeline transportation systems results in a drastic increase of electric power consumption, since, to avoid magnetite precipitation, coal—suspension mixture should be accelerated to substantially higher velocities than coal—water mixture. Another problem is a high erosion wear of pipes and centrifugal pump working wheel caused by highly abrasive particles moving with high velocities. Note that the increase of pipeline stream velocity is accompanied with the squared increase of power consumption (the 3-fold increase of velocity requires the 9-fold increase of power). The abnormally high viscosity of such heterogeneous systems also contributes to the increase of power consumption.
Apart from excessive consumption of power, inevitable use of high speeds for coal hydrotransport assists the intensification of coal wearing-off by high-abrasive magnetite and, therefore, the degradation of coal delivered to the consumer and increase of mechanical losses due to increased dust formation after dry coal withdrawal from the carrier medium.
The increase of coal fines content results not only in the degradation of coal and increase of dusting during all subsequent operations, but aggravates the problems of separating water and paste-like sludge produced in the course of trunk pipeline transportation, of dry coal output, and drastically restricts the possibilities of non-fuel use of coal, e.g., for coke production, as well.
There is no escape from taking into account the fact that the overwhelming majority of fossil coals are methane-containing. Accordingly, during coal destruction, the total coal-contained methane volatilizes and finally comes into the air, which not only decreases substantially the fuel heat capacity, but irreversibly damaging environment as well, since methane, along with refrigerants (Freons) is one of the main destructors of the Earth stratosphere ozone layer.
Also, the presence of solid heaver like magnetite in the carrier medium results in a drastic drop of transport channel throughput rate, because a large portion of pipeline internal volume shall be occupied by foreign solid substance required to increase the carrier density to a level providing the coal lumps flotation, at least in motion.
The water freezing temperature being 0° C., this makes impossible the large-scale use of aqueous magnetite suspensions as carrier media for trunk pipeline transportation of coal in winter. However, for the majority of consumers, the maximum demand for solid fuel falls namely on winter periods; similarly, negative temperatures aggravate the problems of uninterrupted coil delivery by railroad transport due to high freezing of coal in both the railroad cars and outdoor piles.